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A common practice when setting up Load Balancers and creating highly available services is the need to have a keep alive test to ensure the service is up and running well. Normally we monitor servers and alert if they go down then get the relevant people in to fix the issue and restore service. In the world of Citrix NetScalers and high availability this practice does not always suit. More often than not a service will contain more than one back-end server, a single server going down does not always mean a service has failed. However, if both servers in a HA pair go down then you want to know about it immediately right? This is the issue with Citrix NetScaler and “some” 3rd party monitoring software.
There is a solution to monitoring this that Citrix provide for free called Citrix Command Center (a future post will describe the setup and configuration of this) however if you use a simple monitoring tool to send ICMP echo requests to the Virtual Server vIP then an out the box configuration on the NetScaler will leave you with failed alerting.
The reason behind this is that the NetScaler will respond to ICMP echo requests on behalf of the vIP in the event that all the back end services are down unless you specifically specify otherwise.
To resolve this follow these steps.
- Log into your NetScaler and navigate to Traffic Management – Load Balancing – Virtual Servers
- Double click the Virtual Server you want to edit
- Under the heading “Traffic Settings” click the pencil icon to edit the settings
- Ensure that the “ICMP Virtual Server Response” is set to ACTIVE (This will ensure that the NetScaler responds even if a single service within the Virtual Server is up. If you leave it as PASSIVE the NetScaler will always repond to ICMP Requests)
- Click “Done” to save the Virtual Server
- Navigate to System – Network – IPs
- Find the IP Address for the Virtual Server you edited in the previous step and double click it to open the properties
- in the “ICMP Response” field ensure you have “VSVR_CNTRLD” selected
- Click “Done” to save the IP Properties
Once you have done this your Virtual Server will STOP responding to ICMP echo requests when all of the back-end attached services are in a “down” or “out of service” state.
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